Keeping in step with the recent tremendous developments in information equipment, color LCDs have found wide-spread commercial utility as information display units in all equipment relating to the display of information, for example, as display screens in personal computers, mobile information equipment, television sets, projectors, monitors, car navigation systems, cellular telephones, computers and electronic dictionaries, as displays such as information display boards, guidance display boards, function display boards and sign boards, and also as monitor screens in digital cameras and video cameras. As a consequence, CFs for color LCDs are also required to have still better quality in image characteristics such as sharpness. From the diversification of LCD applications, there is also diversification in size, resulting in an increasing demand for both smaller LCDs and larger LCDs. There is, accordingly, an outstanding demand for the supply of CFs at low cost for all such LCDs.
The fabrication of CFs relies upon a fabrication process called “the photolithographic process” in many instances. To form by this process a pixel pattern of the additive mixing system of three primary colors consisting of red (R), green (G) and blue (B), a photosensitive color resist (photosensitive ink) of one of the colors is coated on a CF substrate by a spin coater. Through a photomask prepared in advance and defining therethrough a light-transmitting pattern conforming with a pixel pattern of the corresponding color, ultraviolet rays are irradiated to cure the coated resist film. Unexposed portions of the coated resist film are then washed off to develop a pixel pattern of the specific color. With respect to each of the remaining two colors, the above-described procedure is repeated to fabricate a CF. The formation of a CF having a pixel pattern of three primary colors consisting of yellow (Y), magenta (M) and cyan (C) can be conducted likewise.
In the above-described photolithographic process, however, the amount of each resist with which its corresponding actual pixel pattern is formed as a result of the application by the spin coater is, for example, as little as only 10% or so of the actually-used amount of the same resist, and the majority of the resist is simply discarded. This is very uneconomical, and correspondingly, the resist with which the pixel pattern is formed is expensive.
With a view to providing a solution to the above-described problem, it has been attempted to reduce the loss of color resists by coating color films over the entire surfaces of plastic films, respectively, and then successively transferring the color films onto a CF substrate; or by applying the color resists onto a CF substrate by slit coaters, respectively. Both of these attempts, however, form pixels by the photolithographic process, and therefore, the problem that many steps are required still remains unsolved.
With a view to rationalizing the fabrication process to improve its economy, it was also attempted to fabricate CFs by a printing method. As the printing with the three RGB colors was performed color by color, misalignments took place among the printed pixels themselves, leading to reductions in the resolution and positional accuracy of the printed pixels. As a result, the CFs so fabricated were insufficient in the fineness, definition and the like of the pixels of the three primary colors.
An object of the present invention is, therefore, to fabricate CFs, which show excellent performance in image characteristics such as pixel fineness and definitions, by a fabrication process which can economically fabricate the CFs at low cost through rationalized steps and can also meet the move toward larger CFs; and also to provide CFs and image displays at low cost.
The present inventors have found that the use of a central impression cylinder press for the formation (printing) of a CF pixel pattern especially via a mask defining therethrough perforations which are in conformity with the pixel pattern makes it possible to form the pixel pattern with extremely high accuracy, to provide a CF of performance excellent in image characteristics such as image fineness and definition, and also to solve the above-described inherent defects of the conventional printing method such as insufficient resolution and positional accuracy.